| Re: 2017 Breakdown & Engine Replacement [message #326289 is a reply to message #326281] |
Thu, 23 November 2017 12:24   |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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Ray Erspamer wrote on Thu, 23 November 2017 10:45No one has been able to give a good reason on why the piston broke. Many say ignition timing, some say over-heating. Even Dick Paterson couldn't give a good reason. I know my timing was set correctly. It remains a mystery.
Ray,
This is Thanksgiving Day, and as my daughter and family are arriving soon, I have to stay clean. That means I can't go out to the shop and work on my own coach. So, I stopped to look at your case in greater detail. While I know I could do better with the parts in my hand and my own microscope, I think I can shed some light on this for you. Even without seeing the crown, there are some good indicators available.
If it makes you feel better, you didn't stand a chance. The critical part of the failure occurred in about three turns of the crank and the entire process was probably less than 100.
Stop for a moment and look at frames A12 and A111. While this is at the pixel limit, both show signs of fatigue. This is particularly evident in lower corner of the break (Piston lower). It is that "clam shell" appearance. The failure started there or possibly in the other corner, but part that looks to me like it happened too fast. Once that crack reached a critical point, that side of the support for the thrust skirt was gone. Then the skirt collapsed and pealed it self off the remaining crosshead (bearing boss) carrying the cast in reinforcement with it.
The rings appear to still be free, so it was not a timing issue causing detonation.
You wrote that there were no marks on the crown, and that is also consistent with not having a timing issue.
The coking under the crown is actually lighter than I might expect given the engine's service. So, it sure was not an over heat problem. Even in an engine equipped with a lube oil cooler, an overheat causes the lube oil to go over usable temperature and it will coke where is can do so.
Well, I'm glad that you were able to wrangle the parts you needed to put a good engine back together.
I hope you also had a good Thanksgiving with friends and/or family.
Matt - the engine lab refugee
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] 2017 Breakdown & Engine Replacement [message #326401 is a reply to message #326284] |
Mon, 27 November 2017 10:57 |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
Karma: -3
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Senior Member |
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I installed a brand new auxiliary engine oil cooler. Radiator is no longer in the circuit.
Ray Erspamer
78 GMC Royale Center Kitchen
403, 3.70 Final Drive
Holley Sniper Quadrajet EFI System,
Holley Hyperspark Ignition System
414-484-9431
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| Re: 2017 Breakdown & Engine Replacement [message #326403 is a reply to message #326289] |
Mon, 27 November 2017 11:02 |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
Karma: -3
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Senior Member |
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Matt, thanks for your great input. It puts my mind at ease knowing it was not detonation or over-heating.
The engine was rebuilt/replaced in 1994 by the previous owner and had 70,000+ miles on it. Timining chain was in fairly good shape, valves were NOT burned but several had recessed seats.
Have a great day.
Ray Erspamer
78 GMC Royale Center Kitchen
403, 3.70 Final Drive
Holley Sniper Quadrajet EFI System,
Holley Hyperspark Ignition System
414-484-9431
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